[XRay][AArch64] Implemented a test for the compile-time sleds emitted, and...

[XRay][AArch64] Implemented a test for the compile-time sleds emitted, and fixed a bug in the jump instruction

This patch adds a test for the assembly code emitted with XRay
instrumentation. It also fixes a bug where the operand of a jump
instruction must be not the number of bytes to jump over, but rather the
number of 4-byte instructions.

Author: rSerge

Reviewers: dberris, rengolin

Differential Revision: https://reviews.llvm.org/D26805

llvm-svn: 287516